This invention relates to a process of non-destructive testing of bodies, particularly for the purpose of locating minute cracks or surface discontinuities from various causes such as stress cracks, quenching cracks, and the like. The invention is particularly concerned with a process of the above type where the object contains ground out areas having smeared metal, and which removes the smeared metal and reveals othr cracks or surface discontinuities.
In many instances, surface cracks in parts or objects are removed by grinding out appropriate areas in welds or parent material. It is accordingly then necessary to remove smeared metal or material remaining on the surface and to locate any residual cracks not previously removed by the grinding operation.
U.S. Pat. No. 3,564,249 discloses a reverse penetrant method and means comprising applying to the surface of a specimen to be inspected, a liquid dye penetrant containing a daylight visible dye, removing excess penetrant from the surface of the specimen, and applying to the surface a developer coating containing a fluorescent material and when viewed under fluorescent light the coating fluoresces uniformly over the surface with dark dye traces whereever residual dye penetrant is entrapped is surface defects, and which stand out in sharp contrast with the brilliance of the fluorescing background coating.
It is an object of the present invention to detect surface cracks in bodies, the surface of which has been previously ground to remove surface cracks, with smeared metal remaining on the surface. Another object is to remove surface cracks remaining beneath the smeared metal by removing such smeared metal by a penetrant solution followed by application of a reversal developer of the type noted above. A still further object is the provision of a process of the type noted above by a simple three step operation employing a penetrant which also functions as an etchant, in conjunction with a reversal developer.